This invention pertains to down hole motor controls. More specifically but not in a limiting sense, it pertains to apparatus that responds to change in the axial relationship of the motor rotor relative to the motor body to change the flow rate of fluid down the drill string relative to flow through the power producing portion of the motor.
During the use of down hole motors, on pipe strings in wells, the rotor can move downward if the motor bearings wear excessively, or if selected motor assembly connections fail. In normal operation the pressure drop through the motor may not change enough, in response to motor trouble, to be detected at the surface. The pressure drop through the motor may be a small fraction of the overall pressure drop in the mud circuit of the overall system. The change in pressure drop through the motor may go undetected until extensive damage has occurred.
Rotor position sensors have been proposed that depend upon instrumentation and complex systems for indication of rotor position change that indicates damage. In the interest of simplicity and reliability, there is need for a failure detection system that depends only upon systems that are a normal part of the essential operation. Further, the detection method needs to be part of the parameters normally indicated and usually recorded.
An arbor is attached to and preferably spins with the motor rotor, having a bore through the rotor shaft, that normally conducts a limited flow of fluid from the top of the rotor to an outlet downstream of the power producing portion of the motor. A valve in the arbor is normally closed and controls a fluid channel that opens into the drilling fluid supply channel upstream of the motor and opens into the motor rotor shaft bore.
A valve actuator is situated to engage a surface on the housing when the rotor moves axially a preselected amount and further movement opens the valve to allow fluid to flow through the bore of the rotor. The pressure drop across the motor is reduced when the rotor bore is added to the fluid flow path. The change in the overall pressure drop in the mud flow circuit is detectable at the surface. That pressure drop is an indication that the motor rotor has dropped more than a preselected amount.
An object of the invention is to provide a change in the pressure drop in the drilling fluid circuit when a down hole motor rotor changes axial position, a preselected amount, relative to the motor body.
Another object is to change pressure drop in the drilling fluid circuit in response to motor bearing failure without changing the motor design.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.